Saadanius hijazensis – New Oligocene Primate sheds light on Divergence of Apes

Saudi Arabia 30 million years ago, looked very different than it does today.  Much of this desert kingdom was a lush and verdant paradise for the rapidly diversifying mammalian species.  Bordering the last remnants of the once mighty Tethys ocean there were extensive mangrove swamps and thriving in this half-way house environment between the land and sea were a number of genera of monkeys and other arboreal creatures.  The discovery of a partial cranium (part of the skull) dating from approximately 28-29 million years ago, may have shed light on the divergence of the apes from Old World monkeys.

In the hills overlooking the Red Sea a team of scientists have unearthed the fossilised elements of a skull of an ancient creature that may be a transitional fossil showing a point in the evolution of apes from monkeys.

The skull could help palaeontologists to answer questions about the life of primates in a geological epoch that until now has provided few fossil clues.  The report on this fossil and its potential implications regarding the evolution of apes is published in the scientific journal “Nature”.

Commenting on the discovery, Iyad Zalmout, a palaeontologist with the University of Michigan and an author of the paper stated:

“It turns out it’s not an ape, it’s not a monkey, it’s something intermediate.”

The expedition were a little surprised to find the fossil, their primary objective being to explore the coastal sediments to excavate ancient whale fossils, helping to piece together the evolution of this particular group of mammals. They were not expecting to find ancient monkey/primate remains, especially skull material which could provide a fresh insight into the evolution of apes from Old World monkeys.

A Photograph of the Skull Material

Picture Credit: Nature/Zalmout et al

The picture shows an anterior view of the skull material (view from the front) on the left and a ventral view (view from the side) on the right.  Although fragmentary, the nasal concha (hole where the nose tissue would be) is clearly visible, along with the nasal bone (links nose to the eyes) and elements of the maxilla.  The face although elongated and angular does have a flattened appearance, a characteristic of apes and of our own hominid ancestors.

This new genus has been named Saadanius hijazensis and it shares morphological features with a family of apes known as the Propliopithecoidea, an ancestor of apes and monkeys that lived more than 30 million years ago.  The fossil record of monkeys from this part of the Cenozoic is particularly poor, arboreal dwelling animals do not generally have a high potential for fossilisation to occur.  This is due to a number of factors but living in a forested environment leads to very few chances of a corpse being fossilised and preserved.  S. hijazensis lacks the advanced sinuses of extant apes and monkeys (collectively called Catarrhines), however, it does have a bony ear tube that was not fully developed in the Propliopithecoidea.

Commenting on the discovery, Erik Seiffert, an anatomist at Stony Brook University in New York said:

“This fossil is really key because it has that bony tube.”

He went on to add that comparison of the bony tube and other features such as the teeth and the forward facing position of the orbit (eye sockets) with those of other primates could help palaeontologists to build up a more complete picture of the ape/monkey family tree.

Zalmout and his co-authors are confident that S. hijazensis could help scientists make sense of “competing hypothesis” about how the shape of Catarrhine skulls changed over time.  One theory put forward by palaeontologists based on the limited fossil evidence found to date is that the Catarrhines developed long, flat faces relatively early on in their evolutionary history.  Other scientists, such as comparative anatomists point out that modern, extant genera such as gibbons, have rounder faces and use this evidence to suggest that long, flat faces evolved much later.

The fragmentary Saadanius fossil has a long, flat face and this discovery has excited scientists as it lends support to the theory suggesting the evolution of the flat face very early on in ape evolution.

Erik Seiffert stated:

“This evidence [Saadanius fossil] very clearly supports the palaeontological point of view.”

However, other scientists warn on the over reliance of fossil evidence to prove a particular theory.  For example, facial features may be distorted over the long preservation and fossilisation process, geological pressure can crush, compact and distort features.  Eric Delson, a palaeontologist from Lehman College of the City University (New York), suggested that fossils may only reflect part of the diversity of a group of particular animals, making it difficult to draw precise conclusions.

All the scientists agree that the discovery of more ancient transitional fossils will help to shed light on the evolutionary relationships between different groups.  Saudi officials, keen to promote tourism have already taken steps to preserve this particular dig site.  This will afford palaeontologists the opportunity to explore the area in more depth, perhaps unearthing more fossils that can indicate how Saadanius moved around its mangrove environment and what it ate.

Delson put it succinctly stating:

“It would be interesting to know whether these primates were beginning to come down from the trees and to know something about what they were eating.”

Welcoming the news that Saudi officials want to preserve the site and to promote fossil tourism Zalmout concluded:

“In my experience, if you find one primate there should be more there.  This will be important to see the whole story about fauna in Arabia and Africa.”

We at Everything Dinosaur look forward to reading about future discoveries.

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